Tungsten trioxide (WO3) has been used in electrochromic devices, catalysts, gas sensors, and for other important applications (for electrochromic devices, see U.S. Pat. No. 5,911,965 to J. A. Bailey entitled “Process for Producing Tungsten Oxide,” which issued Jun. 15, 1998; and J. P. Cronin, D. J. Tarico, J. C. L. Tonazzi, A. Agrawal, and S. R. Kennedy, “Microstructure and Properties of Sol-Gel Deposited WO3 Coatings for Large Electrochromic Windows, Solar Energy Materials and Solar Cells, vol. 29, pp. 371-386, 1993; for catalysts, see M. A. Reiche, P. Hug, and A. Baiker, “Effect of Grafting Sequence on the Behavior of Titania-Supported V2O5—WO3 catalysts in the selective reduction of NO by NH3,” J. Catal., vol. 192, pp. 400-411, 2000; for gas sensors, see U.S. Pat. No. 4,586,143 to M. Kaneyasu et al. entitled “Gas Detecting Apparatus,” which issued Apr. 29, 1986; U.S. Pat. No. 5,811,662 to D. E. Williams et al. entitled “Resistive Gas Sensing, Especially for Detection of Ozone,” which issued Sep. 22, 1998; and X. Wang, N. Miura, and N. Yamazoe, “Study of WO3-Based Sensing Materials for NH3 and NO Detection,” Sensors and Actuators, B, Chemical, vol. 66, pp. 74-76, 2000, all of which are incorporated by reference herein).
The method used for preparing WO3 often depends on the desired application. Methods for preparing thin films, for example, often differ from those used to prepare WO3 in bulk powder form. Thin films of WO3 have been prepared by sputtering, chemical vapor deposition, plasma based methods, spray pyrolysis, and dip coating (for sputtering methods, see, for example, I. Ruokamo, T. Kärkkäinen, J. Huusko, T. Ruokanen, M. Blomberg, H. Torvela, and V. Lantto, “H2S Response of WO3 Thin-Film Sensors Manufactured by Silicon Processing Technology,” Sensors and Actuators B, vol. 18-19, pp. 486-488, 1994; for chemical vapor deposition, see U.S. Pat. No. 4,233,339 to M. Leibowitz entitled “Method for Making Electrochromic Films Having Improved Etch Resistance,” which issued Nov. 11, 1980; for plasma based methods, see U.S. Pat. No. 5,788,738 to S. Pirzada et al. entitled “Method for Producing Nanoscale Powders by Quenching of Vapors,” which issued Aug. 4, 1998; for spray pyrolysis, see M. Regragui, M. Addou, A. Outzourhit, J. C. Bernede, Elb. El Idrissi, E. Beneseddik and A. Kachouane, “Preparation and Characterization of Pyrolytic Spray Deposited Electrochromic Tungsten Trioxide Films,” Thin Solid Films, vol. 358, pp. 40-45, 2000; and for dip coating, see U.S. Pat. No. 5,911,965 to Bailey et al., vide supra, and U.S. Pat. No. 5,525,264 to J. P. Cronin et al. entitled “Precursor Solutions for Forming Coatings,” which issued Jun. 11, 1996, all of which are incorporated by reference herein).
Examples of methods for preparing bulk WO3 powder, and nanosized powder particles in particular, can be found in the following references, all incorporated by reference herein: I. Jimenez, J. Arbiol, A. Cornet, and J. R. Morante, “Structural and Gas-Sensing Properties of WO3 Nanocrystalline Powders Obtained by a Sol-Gel Method from Tungstic Acid,” IEEE Sensors Journal, vol. 2, no. 4, pp. 329-335, 2002; U.S. Pat. No. 5,788,738 vide supra; U.S. Pat. No. 5,984,997 to C. Bickmore entitled “Combustion of Emulsions: A Method and Process for Producing Fine Powders,” which issued Nov. 16, 1999; and M. Akiyama, J. Tamaki, N. Miura, and N. Yamazoe, “Tungsten Oxide-Based Semiconductor Sensor Highly Sensitive to NO and NO2,” Chemistry Letters, pp. 1611, 1991.
There remains a need for a simple, scalable, and inexpensive method for preparing WO3 nanopowder.
Accordingly, an object of the present invention is to provide a simple, scalable, and inexpensive method for preparing WO3 nanopowder.
Additional objects, advantages and novel features of the invention will be set forth in part in the description which follows, and in part will become apparent to those skilled in the art upon examination of the following or may be learned by practice of the invention. The objects and advantages of the invention may be realized and attained by means of the instrumentalities and combinations particularly pointed out in the appended claims.